Atheist / Agostic Debate

I've heard a bunch of quite well-known scientists and other famous people (e.g. Niel deGrasse Tyson, Bill Nye) who have claimed that scientists, to be true to themselves, "must" be agnostic, not atheist. Their defense of this is that since there is no evidence, a decision can't be made one way or the other on the existence of any mythical beings.

Isn't this kind of claim not entirely valid, though? Does there have to be positive evidence either supporting or contradicting something to make a claim about it, or can a staggering (significant...) lack of any evidence -- when evidence would essentially be expected -- defend a similar claim from a negative aspect as well?

It seems to me that saying "there is no specific evidence, therefore: agnostic" is being dishonest to oneself. This brings up arguments like Bertrand's Teapot, IPU, FSM, or even a "square circle". While there isn't any universe-encompassing body of evidence that rules such things out, the complete lack of any evidence of any sort is really just a different kind of evidence, isn't it?

Do you have any unique perspectives, particular experiences, or tidbits to offer to help solve this fluke of reasoning?

I'm not sure why people waffle at the terms. As you say, the very status of unbelief indicates atheism. And I think that there are very few exception that atheists are agnostic. Anyone who understands the basics of the scientific process will admit knowledge sufficient to prove the non-existence of the supernatural is basically impossible. Whereas theism, by it's very definition, is equally gnostic. People who accept the existence of a specific deity must claim knowledge of it's existence or their faith in it's existence would be questionable. Personally, I see almost no value in the term "agnosticism". Once the definition is clear, I don't know that I have ever heard of an agnostic theist or a gnostic atheist. Atheist tend to only claim that there is no reason to believe in any specific claim and theists tend to attempt to provide evidence to support their knowledge. Seems fairly cut and dried.

Just an example that popped into my head on reading your comment, Strega:

Someone who believes in the possibility of a religious being, and despite the lack of evidence, decides yet to believe. In a way, Pascal's Wager fits in here. You can bet on god existing, or bet on him not existing. Technically, you don't *know* either way, but it's what you choose to believe.

As far as my understanding of the alternatives goes, either there are no gods... or there are approximately 3,000 gods, or there is that teapot in orbit, or there are aliens that visit us, or there is a spirit of the Earth, or there is a Flying Spaghetti Monster, or there is a Yoda, or.... etc. To be a theist, you would believe in a god that had some kind of religious structure to it...

Like you say about Dawkins calling himself a 6.9, I've always been willing to accept the deistic argument, since (where we stand now in science) there's no real way to test the hypothesis, nor is there any evidence of absence, since the central tenet is that the deist god does not interfere with the universe. Maybe this is what some agnostics are really referring to, not so much positive agnosticism, but subliminal acceptance of the plausibility of deism?